250 Principles of Plant Culture. 
individual plants of each species were protected and multi- 
plied, or at least were permitted to perpetuate themselves. 
Since the offspring tends to resemble the parent (18), the 
persistent propagation from the best has resulted in more- or 
less- marked improvement. These facts furnish hints for 
the further improvement of plants. 
434. The Variability of Plants Renders their Im- 
provement Possible. In a species of which the individual 
plants are all practically alike, as in many wild plants, we 
can do little in the way of plant breeding, except to give 
treatment that promotes variability (438). Ina species in 
which the individuals manifest different qualities, however, 
we may hope to secure improvement by using the most de- 
sirable plants as parents from which to secure still further 
variability. 
435. Variations are Not Always Permanent. If we 
find a chance seedling of the wild blackberry, for example, 
that has remarkably fine fruit, the plants grown from seeds 
of this fruit are not always equal in quality to the parent. 
The tendency, in such cases, is for the seedling plants to 
revert or go back to the ordinary type of the species, and 
the more marked the variation, the stronger is the tendency 
to reversion. 
436. How to Fix Desirable Variations. A jized va- 
riation, i. e., one of which the progeny resembles the parent 
in all important characters, becomes a variety (21), as this 
word is used with reference to cultivated plants. There are 
two possible ways of fixing a desirable variation: 
(1) By propagating the plant by division (345). This en- 
ables us to maintain a given variation through many gener- 
ations with comparatively little deviation from the form 
